Zoologger: Moustache helps hipster spider catch prey

Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Species: The brown huntsman spider (Heteropoda venatoria)Habitat: Lurks on the ground, tree trunks and rocks, and runs out to overpower prey in the tropics

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Much can be said about the value of having a moustache – but one spider makes a living from it. The brown huntsman (Heteropoda venatoria) sports a fine white moustache that can be seen at night and lures in food.

It hunts at night. It lies in wait until its prey draws near. Then it runs out, sometimes jumping when its victim is close enough. Although it is quite big as far as spiders go – up to about 10 centimetres wide including its legs – there is still a limit to how far it can run and still catch fleeing prey. Any adaptation that draws in its quarry should thus mean more food.

The spider’s conspicuous moustache-like bristles are located below its eyes, forming a whitish stripe on its head that reflects light differently from the rest of the body at night.

The contrast between the moustache and the rest of the spider’s face is based on brightness rather than colour. Recent studies have shown that the brightly coloured bodies of web-weaving spiders such as Nephila pilipes (the giant wood spider) attract unwitting prey to their webs. So I-Min Tso and his team from Tunghai University, Taiwan, conducted field experiments to test whether the huntsman’s moustache was a lure.

Shaving the ‘tache

The team placed spiders randomly in their usual habitats, using thin string to keep them in place. With infrared cameras, they recorded the number of times an insect approached a spider.

By way of comparison, they anaesthetised some of the spiders and gently shaved off their moustaches. The shaved spiders reflected light differently from those with intact stripes, reflecting a contrasting set of wavelengths. They also attracted significantly fewer prey, showing that the stripe does seem to attract insects.

The researchers then made spider dummies that resembled living spiders from the point of view of moths, their most common prey. To do so, they used information from the elephant hawkmoth, the vision of which has been studied in great detail.

“The advantage of dummies is that one can eliminate the often erratic behaviour of spiders and focus on the behaviour of the insects,” says Marie Herberstein, a biologist at Macquarie University in Sydney, Australia.

The results reinforced what the team had found with real spiders. Those with a white stripe attracted significantly more prey than those without one.

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The high diversity of moths that fly at night means predators have evolved various strategies for attracting them: bats fly and chase them down, whereas web-weaving spiders make intricate aerial webs to trap them. And the brown huntsman lazily uses its moustache to get moths to deliver it an easy meal. When a moth flies close to the ground, the spider pounces on the unsuspecting creature and makes a meal of it.

“It is highly possible that the moths have mistakenly regarded the white coloration as a nocturnal blooming flower during their foraging at night,” says Tso.

But the colour patch does not look like a flower shape, says Herberstein: “Shape may be constrained by the available space on the spider’s face.”

The authors think that the curious moustache-like stripe could have a role to play in sexual selection, too, such as in male-female choice or in assessing the quality of males. “We are currently exploring the roles of the moustache in sexual selection,” says Tso. In jumping spiders, for example, bright visual signals in the face area are “sexy”, which can significantly influence mate choice, the researchers say.